Some multi-tenanted buildings such as condominium buildings incorporate a central monitoring system that attempts to establish the individual energy usage of each unit in the building in order to establish a billing system where each unit pays for their individual amount of energy usage. However, systems that have been proposed for the task have several deficiencies. Some proposed systems incorporate BTU meters, which are meters that attempt to measure the precise amount of heat energy consumed by measuring precise inlet and outlet temperatures and the inlet or outlet flow rate. However, some BTU meters are notoriously inaccurate, unreliable and are subject to operations failures during use. Furthermore, BTU meters are relatively complex and expensive. Accordingly, there has been relatively poor adoption of these devices for this purpose. There is currently a need for a system and method of determining the energy usage cost for individual units in multi-tenanted buildings that is reliable, accurate, and cost effective.